Vehicle height adjustment device and vehicle height adjustment method

ABSTRACT

A vehicle height adjustment device has an adjustment bolt ( 30 ) rotatably supported by or fixed to a wheel-side member or a vehicle-body member, and a spring seat member ( 10 ) threadedly engaging with the adjustment bolt. Rotation of the spring seat member is limited by a bump rubber pedestal ( 41 ) (or a coil spring bracket ( 9 )). Displacement of the spring seat member occurs in an axial direction of rotation of the bolt, in accordance with rotation of the bolt. According to the present invention, rotation of the spring seat involved in rotation of the bolt for adjusting the vehicle height can be restricted, and a construction of a vehicle height adjustment mechanism can be simplified so that the number of parts or members of the device is reduced.

This application claims the benefit of PCT International Application No.PCT/JP2005/008473 filed Apr. 27, 2005 and Japanese Application No.2004-132582, filed Apr. 28, 2004 in Japan, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to vehicle height adjustment device andmethod for a suspension system, and more specifically, to such a deviceand method for adjusting the vehicle height by regulating a position ofa spring seat member which abuts against an end portion of a compressioncoil spring interposed between a wheel-side member carrying a wheel anda vehicle-body member.

TECHNICAL BACKGROUND

A vehicle suspension system is known in the art, which has a compressioncoil spring interposed between a wheel-side member and a vehicle-bodymember, wherein upper and lower spring seats are provided forrespectively supporting upper and lower end portions of the spring, andwherein a vehicle height adjustment device is equipped for adjusting thevehicle height by regulating a position of the spring seat.

For example, Japanese patent publication No. 3,193,914 (JP 3,193,914 B)discloses a device for adjusting a vehicle height, which comprises alower lock nut fixedly mounted on a lower arm; an upper lock nutthreadedly engaging with the lower lock nut; a shank with an outerthread extending through the lower lock nut; and a spring seatintegrally formed on the shank. In such a vehicle height adjustmentdevice, the outer thread of the shank threadedly engages with an innerthread of the lower lock nut. The spring seat vertically, moves independence on rotation of the shank.

Further, Japanese patent application laid-open publication No.2000-142062 (JP 2000-142062 A) discloses a device for adjusting avehicle height, which comprises a spring seat holder fixedly mounted ona vehicle-body member, an adjustment bolt extending through the holderand threadedly engaging with the holder, and a spring seat abuttingagainst the tip end portion of the adjustment bolt. In a condition thatthe bolt extends through and threadedly engages with the holder, thebolt rotates so that displacement of the bolt is caused in an axialdirection of rotation. The spring seat is pressed by or released fromthe tip end portion of the bolt, so that the spring seat verticallymoves under guidance of the spring seat holder.

In the vehicle height adjustment device as described in JP 3,193,914 B,the spring seat is integrally mounted on the shank functioning as avehicle height adjustment bolt and is rotated together with the shank inadjustment operation of the vehicle height. However, a resilientrepulsive force of a compression coil spring, which is not rotatable,normally acts on the spring seat. Therefore, in order to smoothly rotatethe spring seat without rotation of the spring, a particular fabricationis required for enabling an end portion of the spring and the springseat to relatively rotate in their contact surfaces. Thus, amanufacturing process of such a vehicle height adjustment devicerequires a number of manufacturing steps or a complicated manufacturingprocess.

On the other hand, the vehicle height adjustment device as described inJP 2000-142062 A has the spring seat and the adjustment bolt separatedfrom each other. A torque of the bolt is converted to a pressure in anaxial direction of rotation of the bolt at a contact point between thebolt and the seat. Therefore, displacement of the spring seat can becaused in the axial direction of rotation of the bolt, without rotationof the spring seat.

However, in a case of such an arrangement, the spring seat and the boltare structurally separated from each other, and therefore, it isnecessary to provide means for guiding the spring seat in the axialdirection of rotation of the bolt and stabilizing a position of thespring seat. Thus, the vehicle height adjustment device as disclosed inJP 2000-142062 A is provided with a spring seat holder in position,which threadedly engages with the bolt and guides the spring seat, inaddition to the bolt and the spring seat. As a result, such a type ofvehicle height adjustment device requires a complicated construction ofthe device and a number of parts or members for the device.

An object of the present invention is to provide vehicle heightadjustment device and method for a vehicle suspension system, which canrestrict rotation of a spring seat associated with rotation of a vehicleheight adjustment bolt and which can simplify a construction of thevehicle height adjustment mechanism, thereby reducing the number ofparts or members for the device.

DISCLOSURE OF THE INVENTION

In order to achieve the aforementioned object, the present inventionprovides a vehicle height adjustment device for a vehicle suspensionsystem having a compression coil spring interposed between a wheel-sidemember carrying a wheel and a vehicle-body member, which regulates aposition of a spring seat member abutting against an end portion of thespring, so as to adjust a vehicle height, comprising:

an adjustment bolt which is rotatably supported by the wheel-side memberor the vehicle-body member and which is able to be fixedly secured tothe wheel-side member or the vehicle-body member; and

the spring seat member which threadedly engages with said bolt,

wherein rotation of said spring seat member is limited by a component ofthe wheel-side member or the vehicle-body member for causing a relativedisplacement of said spring seat member in an axial direction ofrotation of said bolt in accordance with rotation of the bolt, andwherein said bolt is securely fastened to the wheel-side member or thevehicle-body member for fixing a position of said spring seat member.

According to the aforementioned arrangement of the present invention,the spring seat member threadedly engages with the adjustment bolt andthe position of the spring seat member is stabilized by securelyfastening the bolt to the wheel-side member or the vehicle-body member.The relative position between the spring seat member and the bolt is notchanged unless the bolt is rotated. On the other hand, displacement ofthe spring seat member can be caused in the axial direction of rotationof the bolt by rotation of the bolt, when the bolt is released from thewheel-side member or the vehicle-body member. Since rotation of thespring seat member is restricted by the component of the wheel-sidemember or the vehicle-body member disposed in position adjacent to theupper and lower end portion of the spring, the spring seat member andthe bolt move relatively toward each other in the axial direction ofrotation with rotation of a screw in a tightening direction, and moverelatively apart from each other in the axial direction of rotation withrotation of the screw in a loosening direction.

Therefore, according to the present invention, the rotation of thespring seat associated with the rotation of the bolt can be restrictedwithout structural separation of the bolt from the spring seat, and thespring seat holder can be eliminated to simplify the construction of thedevice and to reduce the number of parts or members of the device.

In a preferred embodiment of the present invention, the spring seatmember is provided with a recess with an internal thread (female thread)formed therein, and the adjustment bolt has a screw part to be insertedinto the recess. The screw part is provided with an external thread(male thread) threadedly engageable with the internal thread of therecess. Preferably, a diameter of the screw part is set to be greaterthan that of the shank of the bolt fixedly mounted on the wheel-side orvehicle-body member. More preferably, the core section of the springseat member formed with the recess extends into a hollow inside area ofthe compression coil spring. In the core section, the recess is formedwith the internal thread having a sufficient screw length. If suchdiameter and length of the screw are ensured, the spring seat member canbe further stabilized.

Preferably, the adjustment bolt has a large-diameter screw partthreadedly engaging with the aforementioned recess; a shank with arelatively small diameter connected to or continuous with thelarge-diameter screw part; a small-diameter screw part connected to orcontinuous with the shank; and rotating tool engagement means providedon an end portion of the small-diameter screw part. The large-diameterscrew part, shank, small-diameter screw part and rotating toolengagement means are aligned with one another on an axis of rotation ofthe bolt. The shank is inserted through a through-hole formed in thewheel-side member or the vehicle-body member. The small-diameter screwpart extends from the wheel-side or vehicle-body member on a sideopposite to the spring. A screw-engaging member, such as a nut,threadedly engages with the small-diameter screw part. The bolt isfastened to the wheel-side or vehicle-body member by tightening thescrew-engaging member and is rotated when the screw-engaging member isloosened or released. After the screw-engaging member is loosened orreleased, a rotating tool is engaged with the aforementioned engagementmeans. The bolt is rotated by the tool, whereby the spring seat membercan be moved in an axial direction of rotation. If such an arrangementis applied to the bolt for the lower seat member, the vehicle height canbe adjusted from the underside of the suspension system. This improvesoperability of the vehicle height adjustment. Such an arrangement allowsthe adjustment operation to be performed in the space below thesuspension system, and therefore, works for the vehicle heightadjustment are relieved. It is useful, particularly in a cab-over typetruck which has a cockpit or the like located above the suspensionsystem.

More preferably, a boss portion having the aforementioned through-holeis formed in the wheel-side member or the vehicle-body member. Anannular journal surface can be provided on the adjustment bolt by a stepformed in a transition between the large-diameter screw part and thesmall-diameter shank. It is desirable that the boss portion has a flatbearing surface abutting against this annular journal surface. Fixationof the bolt is further stabilized where the annular journal surface isseated on the bearing surface, and therefore, the positions of thelarge-diameter screw part and the spring seat member can be moreprecisely controlled and stabilized.

In one preferred embodiment of this invention, the aforementionedwheel-side member is a lower arm, and the aforementioned component ofthe wheel-side or vehicle-body member is a bump rubber pedestal or acoil spring bracket. This component may be another appropriate portion,part or member which can function as detent means for limiting therotation of the spring seat member. For example, a protrusion orprojection may be provided on the lower arm so as to restrict therotation of the spring seat member, and it can be used as theaforementioned component of the wheel-side member. The component of thewheel-side or vehicle-body member functioning as the detent means is notlimited to such an element, but can be suitably designed, depending onthe type of the suspension system or the like.

From another aspect, the present invention provides a vehicle heightadjustment device for a vehicle suspension system having a compressioncoil spring interposed between a wheel-side member carrying a wheel anda vehicle-body member, which regulates a position of a spring seatmember abutting against an end portion of the spring, so as to adjust avehicle height, comprising:

an adjustment bolt which is rotatably supported by the wheel-side memberor the vehicle-body member and which is able to be fixedly secured tothe wheel-side member or the vehicle-body member;

the spring seat member which threadedly engages with said bolt; and

rotation restriction means provided on the wheel-side member or thevehicle-body member for restricting rotation of the spring seat memberby abutting against the rotated spring seat member;

wherein said spring seat member is provided with a recess in which athread is formed;

wherein said bolt is provided with a large-diameter screw partthreadedly engaging with said recesses, a small-diameter shank connectedto or continuous with said large-diameter screw part, securing means forreleasably fastening the small-diameter shank to the wheel-side memberor the vehicle-body member, and engagement means for engaging with arotating tool for rotating said shank; and

wherein said shank extends through a through-hole formed in thewheel-side member or the vehicle-body member.

Preferably, the wheel-side member or the vehicle-body member is formedwith a bearing surface, which is in plane contact with a step formed ina transition between the large-diameter screw part and thesmall-diameter shank so as to rotatably carry the bolt on the wheel-sidemember or the vehicle-body member. More preferably, the step forms anannular journal surface which is seated on the bearing surface.

Preferably, the aforementioned securing means co-operates with the stepso as to clamp the wheel-side or vehicle-body member and to fasten thebolt thereto. The aforementioned engagement means is preferablypositioned on the bolt for engagement with a rotating tool on a side ofthe wheel-side or vehicle-body member opposite to the large-diameterscrew part.

The present invention also provides a method for adjusting a vehicleheight with use of a vehicle suspension system, in which a suspensionsystem has a compression coil spring interposed between a wheel-sidemember carrying a wheel and a vehicle-body member, and a position of aspring seat member abutting against an end portion of the spring isregulated so as to adjust a vehicle height, comprising steps of:

releasing and rotating an adjustment bolt rotatably supported on saidwheel-side or vehicle-body member and threadedly engaging with saidspring seat member;

restricting rotation of the spring seat member by abutment of the springseat member against a component of the wheel-side or vehicle-bodymember, for converting a torque exerted on the bolt to a motion of thespring seat member in an axial direction of rotation, thereby causingdisplacement of said spring seat member in the axial direction ofrotation of said bolt; and

securing said bolt on the wheel-side or vehicle-body member.

According to such an arrangement of the present invention, displacementof the spring seat member can be caused in the axial direction ofrotation of the adjustment bolt by rotation of the bolt. The relativedisplacement between the spring seat member and the bolt occurs so as tomove toward each other in the axial direction of rotation when atightening torque is applied to the bolt, whereas it occurs so as tomove apart from each other in the axial direction of rotation when aloosening torque is applied to the bolt. According to such a method foradjusting a vehicle height, a vehicle height adjustment mechanism can beprovided in the suspension system by provision of the bolt on thewheel-side or vehicle-body member, suitable design of the position andshape of the component of the wheel-side or vehicle-body member, andsuitable design of the position and shape of the spring seat member.Therefore, the construction of the vehicle height adjustment mechanismcan be considerably simplified.

Preferably, a through-hole, through which the shank of the bolt can beinserted, is formed in the wheel-side or vehicle-body member, so thatthe shank externally protrudes through the through-hole from thewheel-side or vehicle-body member on the side opposite to the springseat member, whereby the bolt is released, rotated and fastened on theside opposite to the spring seat member. For example, the spring seatmember is a lower seat member supporting the lower end portion of thecoil spring, and release, rotation and fastening of the bolt areperformed from the underside of the suspension system.

The term reading “vehicle-body member” means a sprung member on thesuspension system or a member having its weight supported by the spring.The term reading “wheel-side member” means a member unsprung by thesuspension system or a member on which the weight of the vehicle bodyacts through the spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cross-sectional side elevational view showing aconstruction of a main part of a vehicle suspension system provided witha vehicle height adjustment device according to the present invention;

FIG. 2 is an enlarged cross-sectional view partially showing the vehicleheight adjustment device as shown in FIG. 1;

FIG. 3 is an exploded cross-sectional view of the vehicle heightadjustment device as shown in FIG. 1;

FIG. 4 includes a plan view and a perspective view which show apositional relationship between a lower seat member and a bump rubberpedestal; and

FIGS. 5 and 6 are cross-sectional views illustrating a relativedisplacement between the lower seat member and an adjustment bolt.

BEST MODE FOR CARRYING OUT THE INVENTION

One preferred embodiment of the present invention is described in detailhereinafter, with reference to the accompanying drawings.

FIG. 1 is a partially cross-sectional side elevational view showing aconstruction of a main part of a vehicle suspension system provided witha vehicle height adjustment device according to the present invention,and FIGS. 2 and 3 are an enlarged cross-sectional view and an explodedcross-sectional view partially showing the device as shown in FIG. 1.

In FIG. 1, a main part of a double-wishbone-type suspension system(wheel suspension system) 1 is illustrated. The suspension system isprovided with a lower arm 2, an upper arm 3, a knuckle 4 and acompression coil spring 5. One end portion of the lower arm 2 on a sideof a vehicle body (an inner end portion) is swingably mounted on avehicle-body member 50 by means of a pivot 6, whereas the other endportion of the lower arm 2 on a side of a wheel (an outer end portion)is articulated to a lower end portion of the knuckle 4 by means of aball joint 7. An upper end portion of the knuckle 4 is articulated to anend potion of the upper arm 3 on a side of the wheel (an outer endportion) by means of a ball joint 8. An end portion (not shown) of theupper arm 3 on a side of the vehicle body is swingably carried by thevehicle body, similarly to the lower arm 2. An intermediate portion ofthe knuckle 4 is equipped with a spindle 51. The spindle 51 carries thewheel (not shown) rotatably.

A coil spring bracket 9 is disposed in position adjacent to the balljoint 8 so that the bracket 9 supports the upper end portion of thecompression coil spring 5. The bracket 9, which is fixedly mounted on amember 52 on a side of the vehicle body by a bolt 53, is one ofvehicle-body members. The bracket 9 has a circular top plate 91 and acylindrical cover member 92, and these members 91, 92 define an area inthe bracket 9, which can accommodate a top portion of the spring 5. Acylindrical member 93 integrally formed on the top plate 91 depends froma center part of the plate 91. An annular upper seat member 94, on whichan upper end portion of the spring 5 can be seated, is located aroundthe cylindrical member 93. The member 94 is fixedly secured to the topplate 91 and the cylindrical member 93. A lower surface 95 of the member94 in an annular form constitutes an upper spring seat which abutsagainst the upper end portion of the spring 5 and which bears aresilient repulsive force of the spring 5.

A lower seat member 10 is disposed in vicinity of an upper surface ofthe lower arm 2 so that the member 10 supports a lower end portion ofthe compression coil spring 5. The member 10 has an integrally combinedstructure constituted from a core section 11 and an annular seat section12. The core section 11 extends into an inside hollow section of thespring, and the annular seat section 12 extends over an outer peripheryof the member 10 to surround the core section 11.

A bump rubber 40 is supported by a bump rubber pedestal 41, which isdisposed in position adjacent to the lower seat member 10. The pedestal41 is integrally formed on the lower arm 2. The pedestal 41 is awheel-side member. The pedestal 41 is located in proximity to a linearedge 16 of the annular seat section 12.

In FIG. 2, an enlarged cross-sectional view of the lower seat member 10is illustrated.

The upper surface of the annular seat section 12 is provided with anabutment surface 13 in a form of an annular groove for accommodating thelower end portion of the coil spring 5 at least partially. The lower endportion of the spring 5 is seated on the annular groove formed by theabutment surface 13. The abutment surface 13 constitutes a lower springseat for bearing the resilient repulsive force of the spring 5.

The core section 11 has a recess 14 which opens downward at a center ofthe section 11. The recess 14 has a circular cross-section and aninternal thread 15 is formed on an inside circumferencial surface of therecess 14. An adjustment bolt 30, which can be screwed into the recess14, is fixedly mounted on the lower arm 2.

As shown in FIGS. 2 and 3, the adjustment bolt 30 is provided with alarge-diameter screw part 32 having an external thread 31; asmall-diameter shank 33 having a round cross-section and connected tothe large-diameter screw part 32; a small-diameter screw part 34connected to the shank 33 and having an external thread; and a bolt head35 having a hexagonal cross-section and formed on a lower end portion(tip end portion) of the small-diameter screw part 34. The screw parts32, 34, shank 33 and bolt head 35 are aligned with one another on acenter axis of the bolt 30.

The lower arm 2 is formed with a boss part 20, through which the shank33 can be inserted. The boss part 20 has a boss hole 21 through whichthe shank 33 extends, and a flat bearing surface 22. The bearing surface22 is brought into plane contact with an annular journal surface 36 ofthe large-diameter screw part 32. A hexagonal nut 37 is screwed on thesmall- diameter screw part 34 downwardly extending from the boss hole21. When the part 34 is tightened with the nut 37, the journal surface36 is seated on the bearing surface 22. The journal surface 36co-operates with the nut 37 to clamp the boss part 20 under pressure,whereby the bolt 30 is securely fastened to the boss part 20.

FIG. 4 includes a plan view and a perspective view, which illustrate thepositional relationship between the lower seat member 10 and the bumprubber pedestal 41.

The annular seat section 12 of the lower seat member 10 has arotation-limiting portion 17 in a form of a flat plate. The portion 17is provided with the linear edge 16. The linear edge 16 is positioned inclose proximity to a side surface 42 of the bump rubber pedestal 41. Thelinear edge 16 linearly extends along the side surface 42 of thepedestal 41. If the lower seat member 10 is rotated about the centeraxis of the core section 11, the linear edge 16 abuts against the sidesurface 42 of the pedestal 41. Therefore, the pedestal 41 interfereswith rotation of the member 10. According to such an arrangement,rotation of the member 10 is limited by engagement or abutment of thelinear edge 16 and the side surface 42 of the pedestal 41, so that therelative rotation between the member 10 and the spring 5 is restricted.This allows the member 10 to be formed with a spring tip bearing portion18, which can abut against a tip end 5 a of a wire rod of the spring 5(shown by phantom lines).

FIGS. 5 and 6 are cross-sectional views illustrating the relativedisplacement of the lower seat member 10 and the adjustment bolt 30.

As shown in FIG. 5(A), the large-diameter screw part 32 of the bolt 30is screwed into the recess 14 of the member 10, and the small-diameterscrew part 34 is tightened to the boss part 20 of the lower arm 2 withthe hexagonal nut 37. The position of the member 10 relative to the bolt30 is defined by the depth D of penetration of the screw part 32 in therecess 14. Therefore, the height H of the member 10 relative to thebearing surface 22 of the boss part 20 (i.e., the height of the surfaceon which the compression coil spring 5 is seated) varies in dependenceon the relative rotation of the member 10 and the bolt 30. In FIGS. 5and 6, the height H of the member 10 is indicated as a distance betweenthe lowermost point 13 a of the abutment surface 13 and the bearingsurface 22.

FIGS. 5 and 6 illustrate a method of adjusting a vehicle height withrotation of the adjustment bolt 30. In operation of adjustment of thevehicle height, a rotating tool T1 such as a wrench is fitted on thehexagonal nut 37, and then, the nut 37 is rotated in its looseningdirection so as to release the tightening force of the nut 37 on theboss part 20 (FIG. 5(A)). Subsequently, another rotating tool T2 such asa wrench is fitted on the bolt head 35 and the bolt head 35 is rotated(FIG. 5(B)). As the bolt head 35 is rotated, the bolt 30 is rotated as awhole. The linear edge 16 of the lower seat member 10 engages with orabuts against the side surface 42 of the pedestal 41, whereby itsrotation is limited. Therefore, the member 10 is no longer able torotate and the bolt 30 rotates independently.

When the bolt head 35 is rotated in its loosening direction as shown inFIG. 6(A), the adjustment bolt 30 is displaced with respect to the lowerseat member 10 in such a manner that the large-diameter screw part 32exits from the recess 14. As a result, the height h1 of the lower springseat (FIG. 5(B)) increases to be the height h2.

On the contrary, if the bolt head 35 is rotated in its tighteningdirection, the adjustment bolt 30 is displaced with respect to the lowerseat member 10 in such a manner that the large-diameter screw part 32penetrates into the recess 14. As a result, the height h1 of the lowerspring seat (FIG. 5(B)) decreases to be the height h3 (FIG. 6(B)).

Thus, the height of the vehicle body supported by the compression coilsprings 5 (i.e., vehicle height) can be adjusted by adjustment of theheight H of the lower seat member 10, in correspondence to therotational direction and the rotational motion of the bolt head 35.

After adjustment of the height H of the lower seat member 10, therotating tool T1 is fitted on the hexagonal nut 37 again and the nut 37is rotated in its tightening direction until the nut 37 is tightened tothe boss part 20, whereby the adjusted height h2, h3 of the member 10 isfixed.

As described above, the vehicle height adjustment device of thisembodiment comprises the adjustment bolt 30 supported by the boss part20 of the lower arm 2, and the lower seat member 10 threadedly engagingwith the bolt 30. Since the member 10 is limited in its rotation by thebump rubber pedestal 41, the member 10 vertically moves in accordancewith the rotation of the bolt 30. When the hexagonal nut 37 is tightenedto the bolt 30, the bolt 30 is securely fastened to the boss part 20 ofthe lower arm 2. The position of the member 10 is stabilized by fixingof the bolt 30.

According to such an arrangement, the lower seat member 10 can becarried in a stable condition and the rotation of the member 10 can berestricted, without provision of a particular member for guiding themember 10 and restricting its rotation, such as a spring seat holder.Therefore, the construction of the vehicle height adjustment device canbe simplified, and the number of parts or members thereof can bereduced. Such a simplified construction of the vehicle height adjustmentdevice is superior in its operationality, stability and reliability andit is extremely advantageous in its practical use.

Although one preferred embodiment of the present invention has beendescribed in detail, the present invention is not limited thereto, butmay be modified or changed without departing from the scope of theinvention defined in the accompanying claims.

For example, the present invention may be applied to the upper seatmember for bearing the upper end portion of the compression coil spring,although the aforementioned embodiment has been described with respectto the lower seat member for supporting the lower end portion of thespring. In such a case, rotation of the upper seat member, which mayotherwise occur owing to rotation of the adjustment bolt, is restrictedby the coil spring bracket.

Further, a locking hole (a hexagonal hole or the like) engageable with arotating tool such as hexagonal rod-like spanner may be formed on theend face of the adjustment bolt, although the adjustment bolt in theaforementioned embodiment is provided with the bolt head having ahexagonal cross-section engageable with a rotating tool.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a vehicle height adjustmentdevice and method for a vehicle suspension system having the compressioncoil spring interposed between a wheel-side member carrying a wheel anda vehicle-body member. The apparatus and method of the present inventioncan be advantageously applied, particularly, to a cab-over type truck orthe like having a cockpit and so forth positioned above the suspensionsystem.

1. A vehicle height adjustment device for a vehicle suspension systemhaving a compression coil spring interposed between a wheel-side membercarrying a wheel and a vehicle-body member, which regulates a positionof a spring seat member abutting against an end portion of the spring,so as to adjust a vehicle height, comprising: an adjustment bolt whichis rotatably supported by the wheel-side member or the vehicle-bodymember and which is able to be fixedly secured to the wheel-side memberor the vehicle-body member; and the spring seat member provided with arecess with an internal thread formed therein, which threadedly engageswith said bolt, wherein rotation of said spring seat member is limitedby a component of the wheel-side member or the vehicle-body member forcausing a relative displacement of said spring seat member in an axialdirection of rotation of said bolt in accordance with rotation of thebolt, wherein said bolt is securely fastened to the wheel-side member orthe vehicle-body member for fixing a position of said spring seatmember, wherein said bolt has a large-diameter screw part which isinserted into the recess and which is provided with an external threadengageable with the internal thread of the recess; a shank with arelatively small diameter, which is integral with the large-diameterscrew part and which is inserted through a through-hole formed in saidwheel-side or vehicle-body member; a small-diameter screw partintegrally connected to or continuous with the shank; and rotating toolengagement means integrally provided on an end portion of thesmall-diameter screw part, and wherein a boss portion having saidthrough-hole is formed in said wheel-side or vehicle-body member, andthe boss portion has a flat bearing surface abutting against a stepformed in a transition between said large-diameter screw part and saidsmall-diameter shank.
 2. The vehicle height adjustment device as definedin claim 1, wherein a core section of said spring seat member formedwith said recess extends into an inside hollow section of saidcompression coil spring.
 3. The vehicle height adjustment device asdefined in claim 1, further comprising a screw-engaging memberthreadedly engaging with the small-diameter screw part on a sideopposite to the large-diameter screw part with respect to saidwheel-side or vehicle-body member, wherein said bolt is securelyfastened to said wheel-side or vehicle-body member by a tightening forceof the screw-engaging member and the bolt can be rotated when thescrew-engaging member is loosened.
 4. The vehicle height adjustmentdevice as defined in claim 1, wherein said component of the wheel-sidemember is a bump rubber pedestal.
 5. The vehicle height adjustmentdevice as defined in claim 1, wherein said component of the vehicle-bodymember is a coil spring bracket.
 6. A vehicle height adjustment devicefor a vehicle suspension system having a compression coil springinterposed between a wheel-side member carrying a wheel and avehicle-body member, which regulates a position of a spring seat memberabutting against an end portion of the spring, so as to adjust a vehicleheight, comprising: an adjustment bolt which is rotatably supported bythe wheel-side member or the vehicle-body member and which is able to befixedly secured to the wheel-side member or the vehicle-body member; thespring seat member which threadedly engages with said bolt; and rotationrestriction means provided on the wheel-side member or the vehicle-bodymember for restricting rotation of the spring seat member by abuttingagainst the rotated spring seat member; wherein said spring seat memberis provided with a recess in which a thread is formed; wherein said boltis provided with a large-diameter screw part threadedly engaging withsaid recess, a small-diameter shank integrally connected to orcontinuous with said large-diameter screw part, securing means forreleasably fastening the small-diameter shank to the wheel-side memberor the vehicle-body member, and engagement means for engaging with arotating tool for rotating said shank; wherein said shank extendsthrough a through-hole formed in the wheel-side member or thevehicle-body member; wherein said wheel-side member or the vehicle-bodymember is formed with a bearing surface, which is in plane contact witha step formed in a transition between said large-diameter screw part andsaid small-diameter shank so as to rotatably carry said bolt on saidwheel-side or vehicle-body member, and wherein said step forms anannular journal surface which is seated on said bearing surface.
 7. Thevehicle height adjustment device as defined in claim 6, wherein saidsecuring means co-operates with said step so as to clamp said wheel-sideor vehicle-body member and to securely fasten said bolt thereto.
 8. Thevehicle height adjustment device as defined in claim 6, wherein saidengagement means is positioned on an end portion of said small-diametershank of said bolt for engagement with a rotating tool on a side of saidwheel-side or vehicle-body member opposite to said large-diameter screwpart.
 9. A method for adjusting a vehicle height comprising: providingvehicle height adjustment device for a vehicle suspension system asdefined in claim 1; releasing and rotating said adjustment boltrotatably mounted on said wheel-side or vehicle-body member andthreadedly engaging with said spring seat member; restricting rotationof the spring seat member by abutment of the spring seat member againstsaid component of the wheel-side or vehicle-body member, for convertinga torque exerted on the bolt to a motion of the spring seat member in anaxial direction of rotation, thereby causing displacement of said springseat member in the axial direction of rotation of said bolt; and fixedlysecuring said bolt on the wheel-side or vehicle-body member.
 10. Amethod for adjusting a vehicle height as defined in claim 9, wherein theshank externally protrudes through said through-hole, and said bolt isreleased, rotated and fastened on the side opposite to said spring seatmember with respect to said wheel-side or vehicle-body member.
 11. Amethod for adjusting a vehicle height as defined in claim 10, whereinsaid spring seat member is a lower seat member supporting the lower endportion of said coil spring, and release, rotation and fastening of saidbolt are carried out from the underside of said suspension system.
 12. Amethod for adjusting a vehicle height comprising: providing a vehicleheight adjustment device for a vehicle suspension system as defined inclaim 9; releasing and rotating said adjustment bolt rotatably mountedon said wheel-side or vehicle-body member and threadedly engaging withsaid spring seat member; restricting rotation of the spring seat memberby abutment of the spring seat member against said rotation restrictionmeans, for converting a torque exerted on the bolt to a motion of thespring seat member in an axial direction of rotation, thereby causingdisplacement of said spring seat member in the axial direction ofrotation of said bolt; and fixedly securing said bolt on the wheel-sideor vehicle-body member.
 13. A method for adjusting a vehicle height asdefined in claim 12, wherein the shank externally protrudes through saidthrough-hole, and said bolt is released, rotated and fastened on theside opposite to said spring seat member with respect to said wheel-sideor vehicle-body member.
 14. A method for adjusting a vehicle height asdefined in claim 13, wherein said spring seat member is a lower seatmember supporting the lower end portion of said coil spring, andrelease, rotation and fastening of said bolt are carried out from theunderside of said suspension system.